Systems and methods for controlling risers

Abstract

Systems and methods for controlling movement of an elongated member providing communication between a vessel and a subsea unit are provided. The method can include connecting a positively buoyant member to an elongated member at a first location and connecting a negatively buoyant member to the elongated member at a second location, wherein at least a portion of the negatively buoyant member rests on a seabed when the elongated member is in an operational null position.

What is claimed is: 
     
       1. A method for controlling movement of an elongated member providing communication between a vessel and a subsea unit, comprising:
 connecting a first end of the elongated member to the vessel; 
 connecting a second end of the elongated member to the subsea unit; 
 connecting a positively buoyant member to the elongated member; and 
 connecting a negatively buoyant member to the elongated member at an attachment point having a fixed longitudinal position between the first end and the second end of the elongated member, wherein at least a portion of the negatively buoyant member rests on a seabed, wherein a portion of the negatively buoyant member forms a pile beneath the elongated member, wherein the positively buoyant member is connected to a first location of the elongated member and the negatively buoyant member is connected to a second location of the elongated member, and wherein a distance between the first location and the second location is less than about 50 meters. 
 
     
     
       2. The method of  claim 1 , further comprising increasing a force provided by the negatively buoyant member as the elongated member moves in a direction away from the negatively buoyant member. 
     
     
       3. The method of  claim 1 , further comprising decreasing a force provided by the negatively buoyant member as the elongated member moves in a direction toward the negatively buoyant member. 
     
     
       4. The method of  claim 1 , further comprising, modifying a force provided by the positively buoyant member by at least one of adding a buoyant material to the positively buoyant member, removing a portion of the positively buoyant member, introducing a fluid to the positively buoyant member, and removing a fluid from the positively buoyant member. 
     
     
       5. The method of  claim 1 , further comprising modifying a force provided by the negatively buoyant member by at least one of adding negatively buoyant material to the negatively buoyant member and removing a portion of the negatively buoyant member. 
     
     
       6. The method of  claim 1 , wherein the distance between the first location and the second location is less than about 3 meters. 
     
     
       7. The method of  claim 1 , wherein connecting the negatively buoyant member to the elongated member comprises connecting the negatively buoyant member to one or more lines and directly connecting the one or more lines to the elongated member. 
     
     
       8. The method of  claim 1 , wherein at least a portion of the negatively buoyant member is in direct contact with the seabed. 
     
     
       9. The method of  claim 1 , wherein the negatively buoyant member is directly attached to one or more pilings or anchors secured to the seabed. 
     
     
       10. The method of  claim 9 , wherein the negatively buoyant member is bolted or welded to the one or more pilings or anchors. 
     
     
       11. The method of  claim 1 , wherein the distance between the first location and the second location is from about 1 meter to about 3 meters. 
     
     
       12. The method of  claim 1 , wherein the elongated member does not rest on the seabed. 
     
     
       13. The method of  claim 1 , wherein at least a portion of the negatively buoyant member is vertically suspended from the elongated member.